Fermentation is a process of anaerobic cellular respiration which consists of glycolysis (ATP is produced) and some extra reactions that make alcohol. Extra reactions include NADH donating its electrons to a derivative of pyruvate, producing ethanol. CO2 is produced when carboxyl group is removed from pyruvate and the remaining molecule is acetaldehyde. During the next step, NADH passes its electrons to acetaldehyde and forming ethanol and NAD+.